The long term objectives of this research are to identify the mechanisms of neuromechanical (NM) impairments underlying postural balance dysfunction in older people, and to establish a scientifically grounded therapeutic program for enhancing balance function and reducing the risk of falls. When human balance is challenged, the stepping reaction is a powerful means of stabilizing the body and preventing falling. Protective stepping is therefore a vital strategy for maintaining balance during activities of daily life. We propose that aging limitations in regional medio-lateral (M-L) hip abductor/adductor (AB/AD) NM responses compromise lateral balance stability by disrupting protective stepping. Consequently, many older people may be particularly vulnerable to lateral instability and injurious falls. Accordingly, our aims involve experimental, modeling, and interventional approaches to understanding these relationships. Aim one is to a) identify the balance perturbation magnitude level at which older subjects transition to a riskier and more problematic crossover protective stepping pattern due to limitations in hip AB/AD NM control as determined by movement kinetics and kinematics;and to b) assess whether balance perturbation magnitude and associated stepping and hip AB/AD NM response measures discriminate between subjects with low fall risk and those with high fall risk. Aim two is to develop and apply a computational model that predicts the balance limits of M-L stepping patterns in relation to regional hip AB/AD NM limitations. Aim three is to assess feasibility factors (compliance, tolerance, benefits) necessary to advance a full-scale therapeutic intervention for preventing falls. We hypothesize that an intervention approach that combines induced step training and hip AB/AD muscle strengthening will demonstrate greater improvements in performance outcomes and fewer prospectively identified falls than either program performed alone. PUBLIC HEALTH RELEVANCE. The relevance of this research to public health lies in its focus on understanding the causes and interventions for minimizing the devastating economic, societal, and personal consequences of age-associated falls.